Switch actuator apparatus



i May 12, 1970 J. E. MCcLAlN ET AL 3,511,944 lSWITCH ACTUATOR APPARATUS 3 Sheets-Sheet l Filed June '5, 1968 FIA m@ m m5 QQ www mmm h umm QQ j; ATTORNEYS May 12, 1970 J. E. MCCLAIN ET AL SWITCH ACTUATOR APPARATUS 5 Sheeizs-Sheeil 5 Filed June 5, 1968 W S a@ N wg@ m wm/ um www d [United States Patent O 3,511,944 SWITCH ACTUATOR APPARATUS James E. McClain, Argus F. Parks, and Maurice A.

Hogue, Greenville, Tex., assignors to Esco Manufacturing Company, Greenville, Tex. Filed June 3, 1968, Ser. No. 734,145 Int. Cl. H01h 5/06 U.S. Cl. 200-17 5 Claims ABSTRACT OF THE DISCLOSURE Improved switch actuator apparatus including arrangement for powering an actuator shaft in both the closed and opened directions, with the requisite power being stored by accumulator means. A differential gear system has an output gear which drives the actuator shaft and an input gear which is driven by a portion of the accumulator means. Latch mechanisms are associated with the input shaft and the planetary gears of the differential gear system, so that when the portion of the accumulator means which drives the input gear is loaded, the actuator shaft may be powered to the closed and opened positions by ordered release of the latch mechanisms.

BACKGROUND OF THE INVENTION The present invention involves improvements in switch actuator apparatus of the type capable of powering a switch actuator in both the closed and opened directions with the requisite power being stored by accumulator means. The present invention also involves improvements in actuating mechanism for vacuum interrupters of the type having coaxially disposed contact carrier rods one of which is fixed and one of which is reciprocable.

BRIEF DESCRIPTION OF DRAWINGS FIG. l is a schematic perspective View, partially cutaway and partially in section, showing switch actuator apparatus in accordance with a preferred embodiment of the invention; FIG. 2 is a schematic longitudinal section view showing the vacuum interrupter in the contact opened position, together with the drive rod and associated parts including crank-connecting rod link-slide arrangements and means linking the driven rotary shaft to the crank shaft; FIG. 3 is a View similar to that of FIG. 2, but with the vacuum interrupter contacts in the closed position and the other parts disposed accordingly; FIG. 4 is a schematic fragmentary front elevational view, partly in section, showing the differential gearing system and its input and output shafts and associated parts; FIG. 5 is a fragmentary schematic side elevational view showing the differential input shaft in the latched position with the associated accumulator means loaded; and FIG. 6 is a schematic fragmentary front elevational View showing a modification of the arrangement shown by FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENT In FIG. l of the drawings there is shown an overall perspective view of switch actuator apparatus in accordance with a preferred embodiment of the present invention. The apparatus is mounted in a housing, which is shown as a rectangular box 11 having a bottom 12, left and right sidewalls 13, 15 and left and right endwalls 17, 19 (as viewed in FIG. 1). The housing is a conventional metal structure having requisite structural integrity. The housing will have a conventional top closure (not shown).

A differential gear system 21 has a casing 23, including left and right sidewalls 25, 27, which may extend 3,511,944 Patented`May 12, 1970 ice input shaft 39" which is journalled at 41 in the casing 23 and at 43 inthehousing left sidewall 13. The input shaft 39 extends outwardly through the housing left sidewall 13. Fixed onto the input shaft 39 adjacent the housing left sidewall .exterior is a crosshead -45 which extends radially outwardly from said shaft in opposite directions. Journalled on the input shaft 39 at 47 immediately outboard of the crosshead 45 is an accumulator loading lever 49. The loading lever 49 is retained on the input shaft 39 by a collar 5 1.

A rst accumulator means includes first and second sets of compression springs. As shown, the first compression spring set 53 is made up of two compression springs 55, each of which surrounds a respective guide rod 57. The guide rods are pivotally connected at one end portion at 59v to one outer end portion of the crosshead 45 and are slidably retained adjacent their other end portions in respective bores in a boss 61 which is fixed to the loading lever 49. The second compression spring -set as shown, is made up of two compression springs 63, each of which surrounds a respective guide rod 65. The guide rods are pivotally connected at 67 to the outer end portion of the crosshead 45 and extend within respective cylinders `69 which contain the springs. The cylinders are pivotally connected at their closed ends at 71 to a boss 73 which is xed to the loading lever 49. The compression springs set are loaded (compressed) when the crosshead 45 is held against rotation and the loading lever 49 is moved in the clockwise direction (as viewed in FIG. l). A stop 75 fixed to the housing left sidewall 13 abuts the boss 61 on the loading lever 49 to limit the clockwise motion of the loading lever. A lock pin 77 cooperates with a projection 79 on the housing left sidewall 13 to selectively retain the loading lever 49 in its maximum clockwise position.

Latch means for the input shaft 39 includes a latch bar which may be regarded as a portion of the crosshead 45 having a latch finger 83. A roller Akeeper 85 is mounted to the left sidewall 13 of the housing and is disposed to cooperate with the latch finger 83. The roller keeper I is spring biased to the latch position, and may 'be moved by means of a cam lever 87 against the spring bias to the latch release position. A stop member 89 fixed to the housing left sidewall 13 cooperates with a stop member 91 on the crosshead 45 to limit the travel of the crosshead in the clockwise direction.

Latch means for the planetary gears 37 includes a latch bar fixed to the planetary gear support and having a latch finger 93 which projects outwardly from a slot in the casing 23. A roller keeper 95 is mounted on the housing left endwall 17 and is disposed to cooperate with the latch finger 93. The roller keeper 95 is spring biased to the latch position and may be moved by means of a cam lever 97 against the spring bias to the latch release position. The cam lever 97 may be actuated automatically by the lever arm 99 of a fault sensing device 101.

The output gear 35 of the differential system 21 is fixed to a driven rotary shaft 103 which is journalled on the casing at 105 and on the housing right sidewall at 107. Second accumulator means include a compression spring 109 which surrounds a portion of a guide rod 111. The guide rod extends through the axially aligned bores of a pair of spaced bosses 113, 115, which are fixed to the housing bottom 12 and extend upwardly therefrom. The guide rod 111 is pivotally connected at one end to a link member 117 which in turn is pivotally connected at 119 to the free end of a crank arm 121 which in turn is fixed to the driven shaftu103, A collar 123 is fixed to the guiderod 111 so that the collar will move to compress the spring 109 when the guide rod is moved in the direction away from the driven rotary shaft 103. The relation of the driven rotary shaft 103, the crank arm 121, the. link member 117 and guide rod 111 is such that the spring 109 is compressed whenthe driven rotary shaft 103 is in the contact closed position.

In FIGS. l, 2 and 3 there is shown a conventional vacuum interrupter 125 of the type having coaxially disposed contact carrier rods 127, 129, with a contact 131 at the end face of each rod. The vacuum interrupter has a cylindrical housing 133 having left and right endwalls 135, 137. A support structure 139 which carries the vacuum interrupter 125 and portions of the interrupter actuator mechanism includes a first mounting pad 141, a rst insulator base 143, a first insulator 145, a first box section 147, a second box section 149, a cylindrical section 151, a second insulator 153, a second insulator base 155, and a second mounting pad 157. The mounting pads 141, 157 may be metal blocks fixed as by welding to the respective housing end-walls 17, 19. The insulator 145, 153 are generally cylindrical in shape, are made of ceramic material and have one end portion received by a central bore of a respective base 143, 155 and fixed thereto by a suitable adhesive. The insulator bases are fixed to the respective mounting pads by means of bolts 159. The first box section 147 has a left endwall 161 and left and right sidewall 163, 165, and is open at top and bottom. The second box section 149 has left and right endwalls 167, 169, left and right sidewalls 171, 173 and is open at top and bottom. The cylindrical section 151 has a cylindrical portion 175, left and right endwalls 177, 17 9 and an intermediate wall 181. The box sections 147, 149 and the endwall and intermediate wall of the cylindrical section 151 may all be made of metal. The cylindrical portion 175 of the cylindrical section 151 is made of insulating material, preferably nonfrangible. The right end of the first insulator 145 is received by a collar integral with the first box section left endwall 161 and is secured thereto by adhesive. The sidewalls 163, 165 of the first box section 147 are fixed to or made integral with the left endwall 167 of the second box section 149. The right endwall 169 of the second box section is fixed in abutting relation to the left endwall 177 of the cylindrical section 151. The left end of the second insulator 153 is received 'by a collar integral with the right endwall 179 of the cylindrical section 151 and secured thereto by adhesives. The pads, bases, insulators, box sections, and cylindrical section which make up the support structure 139 are all disposed in mutual axially alignment.

The vacuum interrupter 125 is mounted within the cylindrical section 151 of the support 139, having its left endwall 135 disposed in abutting relation to the cylindrical section left endwall 1'77 and se-cured thereto by bolts 183 which extend through the second box section right endwall 169. The right endwall 137 of the vacuum interrupter 125 is disposed in abutting relation to the intermediate wall 181 of the cylindrical section 151.The vacuum interrupter fixed contact carrier rod 129 extends through the intermediate wall 181 and into the space betweenthe intermediate wall and the cylindrical section right endwall 179. The vacuum interrupterreciprocable contact carrier rod 1'27 extends through the left endwall 177 of the cylindrical section and the abutting right endwall 169 of the second box section 149. Connections from the vacuum interrupter 125 to the circuit to be interrupted are made via respective flexible conductors 185, 187 which are clamped at one end to respective contact carrier rods 127, 129 and fixed at the other end to the conductors 189 of respective bushings 191, 193 which are mounted on the bottom 12 of the housing 11,

The vacuum interrupter actuatingmechanism includes a drive rod 195 which is disposed coaxially of the contact carrier rods 127, 129 vand is coupled at one end, as by a sleeve 197, to the free end of the movable contact carrier rod 127. The drive rod 195 extends from the coupling sleeve 197, which is located inside the second box section 149, to just beyond the left endwall 161 of the first box section 147. The drive rod 195 is supported for reciprocable motion by respective journals 199, 201 in the left endwalls 161, 169 of the first and second box sections 147, 149. A crank203 is made up of spaced parallel disk members 205 each having a lcentrally disposed stub shaft 207 extending outwardly therefrom. The stub shafts 207 are axially aligned and are journalled in the respective left and right sidewalls 163, of the first box section 147 and form a crank shaft whose axis is disposed transverse to and intersects the axis of the drive rod 195. The disk members 205 are held in spaced parallel relation by a bridge member 209 to which there is fixed a crank lever 211 which extends downwardly beyond the open bottom of the first box section 147. The crank lever 211 has its free end pivotally connected at 213 to one end of an insulating link member 215 which in turn is pivotally connected at its other end at 217 to the free end of a crank arm 219 which is fixed to and extends radially outward from the driven rotary shaft 103. Respective left and right stop bars 221, 223 bridge between the left and right sidewalls 163, 165 of the first box section 147 at the lower margin portions thereof. The stop bars 221, 223 limit the angular motion of the crank lever 211. Left and right slide blocks 225, 227 are mounted on the drive rod on opposite sides of the crank shaft axis ofthe crank 203. A first pair of connecting rod links 229 is pivotally connected to the disk members 205 and to the right slide block 227. A second pair of connecting rod links 231 is pivotally connected to the disk members 205 and the left slide block 225. Ay compression spring 233 surrounds a portion of the drive rod 195 and is fixed at one end to the right slide block 227 and at the other end to a first collar 235 which in turn is fixed to the drive rod 195. A second collar 237 is fixed to the drive rod 195 on the left side of the left slide block 225.

With reference to the crank 203 the respective radii between the crank shaft axis and the respective pivot axis of the connecting link pairs 231, 229 on the disk members 205 may be regarded as respective left and right crank arms. When the crank lever 211 abuts the right stop bar 223, the driven rotary shaft 103 is at its maximum clockwise position (as viewed in FIG. 1),'the axis of the left crank arm is aligned with the axis of the second pair of connecting rod links 231 and parallel to the axis of the drive rod 195, the left slide block 225 is abutting the second collar 237, the drive rod 195 is at its maximum leftward travel, and the contacts 131 are in the opened position. When the crank lever 211 abuts the left stop bar 221, the driven rotary shaft 103 is at its maximum counterclockwiseposition, the axis of the right crank arm is aligned with the axis of the first pair of connecting rod links 229 and parallel to the axis of the drive rod 195, the right slide block 227 has moved relative to the first collar 235 so that thecompression spring 233 is loaded, the drive rod 195 is at its maximum rightward travel, the left slide block 225 is spaced from the second collar 237, and the contacts 131 are in the closed position.

Theoperation of the apparatus will now be described, starting with the appaartus in its inactive state as shown in FIG. l, the vacuum interrupter contacts being opened. First, the lock pin 77 is released and the accumulator loading lever 49 is r'otated counterclockwise until the latch finger 83 engages the roller keeper 85 to place the crosshead 45 in the latched position. Then the accumulator loading lever 49 is rotated clockwise to the stop 75 and the lock pin 77 is re-engaged. As the accumulator loading lever 49 is :moved in the clockwise direction, thespring sets 55, 69 are loaded (compressed). While the accumulator loading lever -49 was being rotated counterclockwise to the latch position of the crosshead 45, the driven rotary shaft 103 was prevented from rotation, since it would tend to rotate in the clockwise direction but could not because the crank lever 211 was already abutting the right stop bar 223. At the same time, the planetary gears 37 will be moved in the counterclockwise direction so that the latch finger 93 will engage the roller keeper 95 to place the planetary gears 37 in the latch position at the same time the crosshead 45 is placed in its latch position. Since the input shaft 39 is prevented by the latch 83, 85 from clockwise rotation as the accumulator loading lever 49 is rotated clockwise, there is no movement of either the planetary gears 37 or the driven rotary shaft 103 while the accumulator spring sets 55, 69 are being loaded.

Now, to close the vacuum interrupter contacts 131, the cam lever 87 is pulled, drawing the roller keeper 85 away from the latch finger 83, permitting the crosshead 45 to rotate clockwise under the power of the compressed accumulator spring sets 55, 69 until the stop members 89, 91 abut. The input shaft 39' will of course move clockwise through the same angular travel. Clockwise rotation of the input shaft 39 will tend to move the planetary gears 37 clockwise also, 1but they are held against clockwise rotation by the latch 93, 95, so that the driven rotary shaft 103 will be rotated in the counterclockwise direction. Rotation of the driven rotary shaft 103 in the counterclockwise direction will cause the crank lever 211 to rotate in the clockwise direction from a lirst predetermined angular position abutting the right stop bar 223 to a second predetermined angular position abutting the left stop bar 221. Movement of the crank lever 211 will cause the disk member 205 to rotate 1n the same direction so that, in effect, the crank shaft (stub shafts 207) and the left and right crank arms of the crank 203, will rotate through the same angular travel as that of the crank lever 211. As a consequence, the connecting rod links 229, 231, slide blocks 225, 2 27, compression spring 233, collars 237, 235, and drrve rod 195 are all moved to the positions hereinbefore described for the condition when the driven rotary shaft 103 is at its maximum counterclockwise position (see FIG. 3) and the vacuum interrupter contacts 131 are in the closed position.

As the driven rotary shaft 103 is rotated counterclockwise, the crank arm 121 will also -be rotated in the counterclockwise direction, causing the guide rod 111 and collar 123 to move 'm the direction to compress the spring 109 and thus loading what may be termed a second accumulator means (the spring sets 55, 69 and related parts may be termed a first accumulator means).

Now, to open the vacuum interrupter contacts 131, the cam lever 97 is operated to Withdraw roller keeper 95 away from the latch nger 93, permitting the planetary gears 37 to be moved under the power of the loaded spring 109. Actually, the force of the spring 109 will move the guide rod 111 in the direction toward the housing left endwall 17, causing the crank arm 121 to rotate in the clockwise direction, and causing the planetary gears 37 to also move in the clockwise direction. At the same time there is a tendency for the input shaft 39 to move in the counterclockwise direction, but it will not do so because the spring sets 55, 69 are preloaded sufficiently to prevent such movement. Consequently, the crank arm 121 will drive the driven rotary shaft 103 in the clockwise direction, causing the crank lever 211 to be rotated from its second predetermined position abutting the left stop bar 221 back to its first predetermined position abutting the right stop bar 223. This movement of the crank lever 211 will cause the disk member 205 to rotate in the same direction so that, in effect, the crank shaft (stub shafts 207) and the left and right crank arms of the crank 203, rwill rotate through the same angular travel as that of the crank lever 211. As a consequence, the connecting rod links 229, 231, slide blocks 225, 227, compression spring 233, collars 237, 235, and drive rod are all moved to the positions hereinbefore described for the condition when the driven rotary shaft 103 is at its maximum counterclockwise position (see FIG. 2) and the vacuum interrupter contacts 131 are in the opened position.

If desired, the arrangement shown by FIG. 4 of the drawings may be modified as shown by FIG. 6. This modification consists of fixing the crank arm 121 to the planetary gear support with the crank arm 121 depending through a slot in the casing 23, instead of to the driven rotary shaft 103. Now, the spring 109 will be loaded at the same time the spring sets 55, 69 are loaded, and the driving force from the crank arm 121 to cause opening of the vacuum interrupter contacts 131 will be applied to the planetary gears instead of to the driven rotary shaft 103. Otherwise, the operation of the apparatus is unchanged.

Switch actuator apparatus constructed in accordance with the principles of the present invention embodies a number of significant advantages. The portion of the apparatus involving the differential gear system, first and second accumulator means, and the latch means for the input shaft and the planetary gears provides an advantageous arrangement for powering an output shaft selectively in both the switch closing and switch opening directions. This arrangement is mechanically, true trip free and is characterized by simplicity, trouble free operation, and ease of operation and adjustment.

Apparatus embodying the principles of the present invention can achieve a closing and opeining action for vacuum interrupter contacts which is particularly advantageous. It may be noticed that the crank 203-connecting rod link 229-slide block 227 arrangement produces nonlinear acceleration motion for the slide block 227 when the crank 203 is rotated through the angular travel provided for the contact closing action. During the first portion of the angular travel, the slide block 227 is accelerated very rapidly, and the inertia of the drive rod 195 and parts fixed to it, causes the slide block to move relative to the drive rod so as to compress and load the spring 233 suiciently that when the movable contact carrier rod 127 reaches the closed contact position the tendency for it to rebound will be overcome by the force of the spring 233, so that there is no contact bounce. This is a very important advantage. Further, as the slide block 227 nears the end of its travel, the leverage available from the crank 203-connecting link 229 combination becomes progressively greater, so that the spring 233 may be loaded suliiciently to exert and maintain a desirable degree of contact pressure. This is also an important advantage. In addition, the collar 235 may be readily adjusted to provide any desired degree of preloading for the spring 233 to meet varying conditions.

When the crank 203 is rotated through the angular travel provided for the contact opening action, the acceleration of the slide block 227, is at first relatively slow, While the spring 233 is being partially unloaded. But at the same time the acceleration of the other slide block 225 is very fast, so that the slide block 225 strikes the collar 237 a sharp hammer-like blow that causes the contacts 131 to positively break and separate very rapidly.

The foregoing disclosure and the showings made in the drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense.

What is claimed is:

1. In switch actuator apparatus utilizing accumulator means and wherein the engagement and disengagement of the switch contacts are effected by the movement of a 7 driven rotary shaft powered by the accumulator means, the improvement which comprises:

(a) a differential gear system including an input gear,

an output gear, and planetary gears;

(b) means connecting said output gear to the driven rotary shaft;

(c) means connecting said input gear to an input shaft;

(d) first accumulator means connected to said input shaft;

(e) latch means for said input shaft;

(f) latch means for said planetary gears;

(g) second accumulator means; (h) means for rotating said input shaft in a rst direction from a stop position to its latch position; (i) means for preventing rotation of said driven shaft while said input shaft is being rotated to its latched position so that said planetary gears will simultaneously be driven to their latch position;

(j) means for loading said first accumulator means while said input shaft is in its latched position;

(k) means for releasing said input shaft from its latched position, whereupon said input shaft will be powered by said first accumulator means to rotate in the opposite direction to its stop position, while said planetary gears will remain fixed, so that said driven shaft will be rotated in the first direction to actuate the switch to its closed position;

(l) means for releasing said planetary gears from their latched position, whereupon the driven shaft will be powered by the second accumulator to rotate in the opposite direction to actuate the switch to its opened position while the planetary gears are also rotated in the opposite direction and the input shaft remains in its stop position. t

2. The switch actuator apparatus as defined by claim 1,v

wherein said second accumulator means is connected to said driven shaft and is loaded as said driven shaft is rotated in said first direction.

3. The switch actuator apparatus as defined by claim 1, wherein said second accumulator is connected to said planetary gears and is loaded as said planetary gears are being rotated to their latched position.

4. Actuating mechanism for a vacuum interrupter of the type having coaxially disposed contact carrier rods one of which is fixed and the other of which is reciprocable, with a contact at the end face of each rod, the contacts being disposed coaxially of said rods and having their face surfaces in substantially parallel planes that are normal to the rod axis; said actuating mechanism comprising:

(a) a drive rod disposed coaxially of said contact carrier rods and coupled at one end to the free end of the movable contact carrier rod;

(b) journal means supporting said drive rod for reciprocable motion;

(c) slide means mounted to said drive rod and slidable thereon in the drive rod axial directions;

(d) a crank having crank shaft means journalled for rotation about an axis transverse to and intersecting said drive rod axis, and crank arm means;

(e) connecting rod link means pivotally connected at one end portion to said crank arm means and at the other end portion to said slide means, with the axes of said connections being parallel to the axis of said crank shaft means;

(f) means for rotating said crank shaft means from a first predetermined angular position of the radius of said crank arm means to a second predetermined angular position of said crank arm radius wherein said radius is parallel to said drive rod axis;

(g) spring means fixed at one end portion against movement relative to said drive rod and fixed at the other end portion against movement relative to said slide means such that motion of said slide relative tosaid drive rod in the direction toward said contacts will load said spring means;

(h)'the relationship between said crankI arm mean and said ,connecting rod link means being chosen such that movement of said crank arm means from said first predetermined angular position to said second predetermined angularl position will produce movement of said slide in the direction of said contcts a distance sufficient to close said contacts and then load said springlsufiiciently to establish and maintain a desired pressure on said contacts.

5. ,Actuating mechanism fora vacuum interrupter of the type having coaxially disposed contact carrier rods one of which is fixed and the other of which is reciprocable, with a contact at the end face of each rod, the contacts being disposed coaxially of said rods and having their face surfaces in substantially parallel planes that are normal to the rod axis; said actuating mechanism comprising:

(a) a drive rod disposed coaxially of said contact carrier rod and coupled at one end to the free end of the movable contact carrier rod;

(b) journal means supporting said drive rod for reciprocable motion;

(c) first slide means mounted to said drive rod and slidable thereon in the drive rod axial directions;

(d) a crank having crank shaft means journalled for rotation about an axis transverse to and intersecting said drive rod axis, and first and second crank arm means;

(e) first connecting rod link means pivotally connected at one end portion to said first crank arm means and at the other end portion to said first slide means, with the axes of said connections being parallel to the axis of said crank shaft means;

(f) means for rotating said crank shaft means from va first predetermined angular position of the radius yof said first crank arm means to a second predetermined angular position of said first crank arm radius wherein said radius is parallel to said drive rod axis;

(g) spring means fixed at one end portion against movement relative to said drive rod and fixed at the other end portion against movement relative to said first slide means such that motion of said first slide relative to said drive rod in the direction toward said contacts will load said spring means;

(h) the relationship between said first crank arm means and said first connecting rod link means being chosen such that movement of said first crank arm means from said first predetermined angular position to said second predetermined angularposition will produce movement of said first slide in the direction of said contacts a distance sufficient to close said contacts and then load said spring sufiiciently to establish and maintain a desired pressure on said contacts;

(i) second slide means mounted to said drive rod on the side of said crank-shaft opposite from -said first slide means and slidable thereon in the drive rod axial directions;-

.(j) second connecting rod link means pivotally connected at one-end portion to said second crank arm means and at the ,other end portion to said second slide means, with the axes of said connections being parallel to the axis of said crank shaft means;

(k) the relationship` between said second crank arm means and said second connecting rod means being substantially the same as that between said first crank arm means and said first connecting rod means; l

(l) boss means disposedv on said drive rod and spaced from said second slide means a distance such that said boss means `will receive an impact blow from said second slide means as said drive rod is moved through the interrupter contact opening stroke;

9 (m) means for rotating said crank shaft means from said second predetermined angular position of the radius of `said irst crank means which is also the rst predetermined angular position of said second crank arm means to a second predetermined angular position of the radius of said second crank arm means wherein said last mentioned radius is parallel to said drive rod axis and said contacts are in the opened position.

10 References Cited UNITED STATES PATENTS 3,287,512 11/1966 Gertsch et a1. 200-17 XR 3,306,207 2/ 1967 Becker et al. 200-17 XR ROBERT K. SCHAEFER, Primary Examiner I. R. SCOTT, Assistant Examiner 

